Non-polymer catechins were reported to have an effect of suppressing an increase in cholesterol level (refer to Patent Document 1, for example). In order to obtain such a physiological effect, an adult is required to drink four to five cups of tea a day. Therefore, there has been a growing demand for the development of a technology capable of incorporating non-polymer catechins at a high concentration in beverages in order to facilitate the ingestion of a large amount of non-polymer catechins.
For the incorporation of non-polymer catechins at a high concentration in a green tea beverage, there is a method of extracting a large amount of catechins from green tea leaves. It is also possible to add non-polymer catechins to a beverage in the dissolved form by making use of a concentrate of a green tea extract (refer to Patent Document 2, for example).
The method of extracting a large amount of catechins from green tea leaves, however, has the problem that the bitterness and astringency emanated from green tea leaves are prone to become stronger if the extract is prepared at a high concentration.
The bitterness and astringency emanated from green tea leaves are thought to stem mainly from non-polymer catechins. It is known that among non-polymer catechins, catechins in the free form taste less astringent but bitter; catechins in the ester form taste both bitter and astringent; and the bitterness and astringency of catechins in the ester form are stronger than those of catechins in the free form.
For improving the extraction efficiency of a green tea component, methods of pulverizing tea leaves and then extracting them are known (Patent Documents 3 to 5).
However, none of the green tea extracts obtained by the above-described method, which contains non-polymer catechins at a high concentration, are still not satisfactory when used as a beverage to be taken for a long term.
[Patent Document 1] JP-A-S60-156614
[Patent Document 2] JP-A-S60-13780
[Patent Document 3] JP-A-S47-5294
[Patent Document 4] JP-A-S52-39476
[Patent Document 5] JP-A-H03-108444
[Disclosure of the Invention]
In the invention, there is thus provided a preparation process of a green tea extract, which comprises subjecting enzyme-inactivated raw tea leaves to CTC processing, drying them until their water content becomes 20 wt. % or less, and then extracting the resulting tea leaves under the condition that the weight ratio of an extraction solvent to the tea leaves to be extracted is 30 or less.